While man has mastered travel on land, sea and air, there still exists, in travel through or across any of the three, some risk of peril. Although trained drivers, captains and pilots may have worked for years to develop their skill, human error still happens. Further, in the presence of adverse conditions such as bad weather, slight errors or miscalculations may be exacerbated into highly dangerous ones.
As technology advances, computers play a much more active role in aiding vehicle maneuvering. Features such as traction control, braking and steering are often processed at least in part by a car computer chip, for example, and more sophisticated car computers can even detect adverse weather conditions and compensate to help keep a driver safe.
Similarly, the use of feedback control laws to augment the pitch command of an aircraft has been used since the latter half of 20th Century. In terms of modern aircraft, digital control laws are used to implement control laws that use a reference command based on pitch rate, load factor or a combination of thereof. Airspeed in conjunction with a load factor may also be considered as a reference command. In some cases, all three variables are considered as reference command, that is, the load factor, pitch rate and airspeed are considered.
The exemplary illustrative non-limiting implementations provide further safety controls for aircraft. For example, the flight control law of one exemplary illustrative non-limiting implementation computes an augmentation command correction based on a set of flight parameters and on the sensed position of the pilot inceptor. The pilot inceptor may be any of a plurality of devices used in aeronautics industry to serve as an interface with a human pilot, e.g. columns, mini-columns, sticks, control yokes, side-sticks, etc. The augmentation command may be mixed with a direct mode pilot command, which may be sent straight to the pitch control surface actuator. The actuator controls a pitch control surface such as an elevator.
Just as driver operations may be altered by a computer chip in a car to prevent accidents on the road, the augmentation command may perform stability augmentation with some additional protection functions for an airplane, which are designed to avoid some undesirable events, such as: i) stall, ii) stall with icing, iii) buffeting, iv) horizontal stabilizer high load, v) low speed, vi) high pitch attitude, etc.
According to one exemplary illustrative non-limiting implementation, the control law computes a reference command (δlaw) in degrees, which is based at least in part on the position of the pilot inceptor. This function is called command shaping, and the function may change during flight. This reference command may be used both in feed-forward and integral loops: the feed-forward command may be produced based at least in part on a gain multiplied by the reference command (δlaw); the integral command may be based at least in part on the integral of the error difference between either angle of attack (α), or pitch angle (θ), and the reference command (δlaw), multiplied by another gain. Thus, for example, the error may be e=δlaw−α or e=δlaw−θ.
Further, in this exemplary illustrative non-limiting implementation, the feedback loop may also consider a state feedback based on a set of sensed flight parameters such as angle of attack (α), pitch rate (q), pitch angle (θ) and airspeed (u) which may be combined using a set of gains.
The integral, feedback and feed-forward command may be summed to compound the augmentation command, which drives the pitch control and trends to reduce the error e to zero in steady state due to integral feedback.
According to this exemplary implementation, the gains may be computed such that the command augmentation automatically pitches the airplane down when one or more undesirable conditions, such as the ones mentioned above, are detected.
According to a further exemplary illustrative non-limiting implementation, based at least in part on a set of flight parameters, a logic module may be at least partly responsible to define the engagement of a control law in a protection function, such as those mentioned, which may be made dynamically during the flight. In a given flight condition, depending on the protection function performed, the logic module may change the following in the control law: i) all the gains of the control law, ii) the command shaping function that defines the relation between pilot command and reference command δlaw, and/or iii) switch selection between angle of attack (α) or pitch angle (θ) in the integral command. In this exemplary implementation, the shaping function defines a maximum commanded angle of attack or pitch angle, correspondent to a maximum inceptor position, depending on which of them are being fed back in a given instant. This way, it is possible to limit the aircraft envelope as desired, using the same law structure that serves as a variety of protections, in different flight phases.
To define all that, the logic module and command shaping uses a set of parameters, which comprises: height above ground (hAGL), ice detection bit (bIce) and engine throttle lever position (δTLA).
When the logic module is not engaged, this control law may not send any command; i.e., a null augmentation command may be sent.
Also, the gains may change depending on flight envelope parameters and configuration parameters, such as Mach number, altitude, flap position and landing gear position.
Thus, according to one exemplary illustrative non-limiting implementation, either angle of attack or pitch angle are considered as a reference command. Further, the angle of attack and/or pitch angle values are limited inside a permitted flight envelope by means of a command shaping, and gains are changed, adapting one or more protection functions.
In accordance with another exemplary illustrative non-limiting implementation the command shaping, the feedback and feed-forward gains and switches and the integral feedback from angle-of-attack (α) to pitch angle (θ) are changed.